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An Xcode 4 template to create universal static libraries

I’ve created an Xcode 4 project template to create universal (armv6, armv7 and simulator) static libraries for iOS, based on Adam Martin’s script:

iOS-Universal-Library-Template

The existing static library template provided with Xcode only builds one architecture, which is not particularly suitable for distribution. A number of people have created scripts to create universal libraries, which require some mucking around with Xcode target settings to use.

This template draws on this work to provide all that is required to produce universal libraries – just select the ‘Universal Static Library’ type in the New Project/New Target dialog, and you’re all set.

Universal static library

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The Amazing Audio Engine: Funky Remote IO-based Core Audio Engine Coming Soon

The Amazing Audio EngineHuzzah! I’m announcing a new project which will be launching over the next couple of months.

It’s called The Amazing Audio Engine, and it represents the product of years of experience with iOS audio. It’s a sophisticated iOS audio engine that lets developers skip the Core Audio learning curve, and get on with writing great software.

The tech behind this is what drives Loopy and Loopy HD, as well as the in-development Audiobus app.

Subscribe at theamazingaudioengine.com to be kept in the loop as it approaches launch time.

Some of the features:

  • Automatic mixing of multiple audio signals with per-channel volume and pan controls.
  • Built-in support for audio filtering and effects, including the ability to form complex filter chains, constructing channel groups, or even whole trees of groups, and filtering them as one composite signal.
  • Built-in support for audio input, including optional use of the Voice Processing IO unit, for automatic echo removal – great for VoIP.
  • Record or monitor the output of the whole audio system, for in-app session recording, or get the output of one channel, or any group of channels in the processing tree.
  • Support for any audio format (AudioStreamBasicDescription) that the hardware supports: Interleaved, non-interleaved, mono, stereo, 44.1kHz or any other supported sample rate, 16-bit, 8.24 fixed floating-point – whatever you need for your project.
  • Very light, efficient engine, designed from the ground up for speed. All Core Audio code is pure C; no Objective- C or BSD calls, no locks, no memory allocation.
  • Efficient mixing of input signals, using Apple’s MultiChannelMixer.
  • Fast, lock-free synchronisation mechanism, enabling developers to send messages to the main thread from the Core Audio context, and vice versa, without locking or memory allocation from the Core Audio thread. Message sending from the main thread is two-way, and can be asynchronous, with a response block, or synchronous.
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Talking about Audiobus on a bicycle

Lets have a chat about Audiobus, you and I. Here, you can sit on the handlebars.

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Audiobus action on Tumblr

Audiobus tumblrI’m blogging about Audiobus’s development and other bits and pieces over on the Audiobus Tumblr blog.

If you’re interested to see what I’m up to, do join me over there.

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Some in-progress screenshots of my new project

It’s called “Audiobus”, and — yep, them’s big words — it’s going to change the way people create music on iOS.

Here’re some mockups of the main interface…

Audio Bus Mockup 1

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Subscribe here for more news about Audiobus as it happens.

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Breaking the limits: Storing data bigger than 1 Mb in Google App Engine’s Datastore

Google App Engine is a fantastic platform for hosting webapps, and a great resource for iOS developers who need an online component to their products. It’s hard to believe that the service is essentially free! I’m using it with The Cartographer, but I found myself coming up against a hard limit with the datastore.

You see, the datastore limits entities to 1 Mb. I’m trying to store XML data in there, and sometimes that can exceed the 1 Mb limit.

XML being the verbose creature that it is compresses very nicely, so it occurred to me that if I selectively compress the larger blocks, I should be able to quite easily squeeze in underneath the limit. Sure enough, a 1.6 Mb XML block compressed into about 200 Kb.

App Engine makes it very easy to define custom properties on data models, so I’ve written a CompressibleTextProperty class that automatically compresses/decompresses properties above a certain size. This means that there’s no performance loss for entities that are small enough to fit easily, but still enables the storage of bigger blocks of content.

The alternative was to break entities up into several different database entities, but this sounded like much more work, and sounded much less elegant.

So here’s what I came up with — it’s used the same way the other Property types are used. Read More »

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Easy inclusion of OpenSSL into iOS projects

Oddly, iOS doesn’t provide any OpenSSL implementation at all — If you want to do anything with crypto (like checking signatures, checksumming, etc.), you have to build in the library yourself.

I came across a great XCode project wrapper for OpenSSL yesterday, by Stephen Lombardo. This is an XCode project file that contains a target to build OpenSSL from source, and works with both Mac and iOS projects. I made some modifications to it, in order to make it work by just dropping in the OpenSSL source tarball, without having to dirty up your source tree with the extracted OpenSSL distribution.

Here’s how to use it:

  1. Download the OpenSSL source.
  2. Put the downloaded OpenSSL source tar.gz into the same folder as openssl.xcodeproj (I put it in Library/openssl within my project tree).
  3. Drag the openssl.xcodeproj file into your main project tree in XCode.
  4. Right-click on your project target, and add openssl.xcodeproj under “Direct Dependencies” on the General tab.
  5. On the Build tab for your project’s target, find the “Header Search Paths” option, and add the path:

    $(SRCROOT)/Library/openssl/build/openssl.build/openssl/include

    (Assuming you’ve put openssl.xcodeproj at the path Library/openssl — adjust as necessary).

  6. Expand your target’s “Link Binary With Libraries” build stage, and drag libcrypto.a from the openssl.xcodeproj group.

Then, you can just import and use as normal (#import <openssl/dsa.h>, etc).

Download it here

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Avoid the clobber: Nest your network activity indicator updates

On the iPhone, when you are doing anything that uses the network, you’re supposed to let the user know something’s going on, via -[UIApplication setNetworkActivityIndicatorVisible:]. This takes a boolean.

That’s all well and good, but if you have more than one object in your app that may do things with the network simultaneously, you’re going to clobber yourself.

A nice and easy solution: Maintain an activity counter and create a category on UIApplication to maintain it, and show or hide the indicator as appropriate. Then, whenever you start doing something with the network:

[[UIApplication sharedApplication] showNetworkActivityIndicator];

…And when you’re done:

[[UIApplication sharedApplication] hideNetworkActivityIndicator];

Here’s a category that’ll do it: Read More »

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